A typical arrangement of a video production switching apparatus is schematically illustrated in FIG. 1. In the production switching apparatus of FIG. 1, input video signals are respectively provided to input terminals 50 and 51 from video cameras 1 and 2. A black burst signal is provided to an input terminal 52. Each of the terminals 50, 51 and 52 is connected via cross points to video signal buses A and B. Buses A and B provide the input signals to a mixer/key signal amplifier (MIX/KEY) 55. A key signal generator 54 provides image mixing and changeover control signals to MIX/KEY 55 so that a desired video signal that includes a special effect such as a key or wipe effect is output from MIX/KEY 55. The signal output from MIX/KEY 55 is provided to a superimposing circuit 56 which is also controlled by signals from key signal generator 54 and which receives input character and/or image signals provided at a terminal 53. The character and/or image signals received by superimposing circuit 56 are added as titles and so forth to the video signal output by MIX/KEY amplifier 55 and the resulting signal is supplied to an output signal processing circuit 57. Output signal processing circuit 57 performs waveform shaping of the output signals, which are then provided to output terminals 58 and 59. The output signal at output terminal 58 is transmitted on a main line for broadcasting, while the output signal from output terminal 59 is supplied to the production studio monitor for monitoring the broadcast signal.
In JP Pat. Appln. No. 3-108392, filed on Apr. 13, 1991, and which is commonly assigned with the present application, there is described a special effects apparatus that is capable of conveniently executing complex wipe and mask patterns including effects that give the impression of gradually wiping a clouded glass surface, or of painting a wiped region of a video image so that the image is gradually erased. The special effects apparatus described in Appln. No. 3-108392 is generally illustrated in FIG. 2 and may, for example, be incorporated in MIX/KEY 55 of FIG. 1.
Returning to FIG. 2, the special effects apparatus of the aforesaid Appln. No. 3-108392 includes a key processor 32 and a video memory 37. Key processor 32 includes multipliers 33 and 34 and adders 35 and 36. A key signal K is provided to an input terminal 31 and an input video signal V.sub.1 is provided to an input terminal 30.
The value "1" is supplied to one input of adder 35 and the key signal K is applied in a negative sense to the other input of adder 35 so that adder 35 outputs an inverted key signal 1-K, which is the inverse of the key signal K received at input terminal 31. One input of multiplier 33 receives inverted key signal 1-K and the other input of multiplier 33 receives the input video signal V.sub.1 which is supplied from input terminal 30. The resulting multiplied signal V.sub.2 is provided to an input of adder 36 where it is added to a signal V.sub.3 output from multiplier 34. The resulting sum is stored in the video memory 37 from which it is output as output signal V.sub.4 under control of a paint control signal supplied to a terminal 39. The signal V.sub.4 output from video memory 37 is provided as an output signal at an output terminal 38 and is also fed back to an input of multiplier 34 of key processor 32. Multiplier 34 multiplies the signal V.sub.4 fed back from video memory 37 by the key signal K supplied through input terminal 31 to produce the signal V.sub.3 which, as mentioned above, is added by adder 36 to the signal V.sub.2 output by multiplier 33.
By means of the circuitry of FIG. 2, complicated special effects involving mask patterns, wipe effects and the like can be created in a convenient manner. Referring now to FIG. 3 in combination with FIG. 2, a combined mask pattern such as that shown in FIG. 3 can be created in a multi-step process, in which, for example, first a diamond-shaped mask 23 is used to mask a portion of the image represented by input video signal V.sub.1. The resulting image signal is temporarily stored in video memory 37 without being output via terminal 38 and fed back to key processor 32, and then a second, circular mask pattern 24 is added at the location shown in FIG. 3. Again the resulting image is stored in video memory 37 and fed back to key processor 32 without being output via terminal 38. Thereafter, a small square 25, a star 26 and additional small squares 27 and 28 are added as additional mask patterns in respective steps in which the image resulting from the previous step is fed back from memory 37 and further processed in key processor 32. When all of the desired mask patterns have been added, then the final image, with the complicated mask pattern shown on FIG. 3, is output from terminal 38.
According to another mode of operating the circuitry of FIG. 2, a different sort of effect may be realized by continuously outputting the image stored in memory 37 via output terminal 38 while feeding the stored image back to key processor 32 and varying the key signal K applied at input terminal 31. For example, referring now to FIGS. 4A and 4B in combination with FIG. 2, initially a small circular mask pattern 29 is applied to the image and the mask pattern is then expanded and moved as indicated in FIG. 4A until it has the size and is in the location indicated by large circle 30. With continuous feeding back .of the image signal stored in memory 37, while the image signal is being output via terminal 38, the resulting output image as shown in FIG. 4B includes not only the final mask pattern 32, but also the initial location of the mask pattern 31 along with all the interim positions and sizes of the mask pattern as it was expanded and moved across the image. Such a continuously varying mask pattern can also be used as a wipe pattern.
FIGS. 5A-5E illustrate a gradual and continuously changing wipe effect that can be created using the circuitry of FIG. 2. In FIG. 5A, the dotted outline 39 of a car indicates a location in the video image in which a car, not yet visible in the image, is to be gradually made visible by a wipe effect. In FIG. 5B, an upper left portion 40 of the car image is gradually made to appear, in the manner, for instance, of wiping a clouded glass, by dynamically changing the configuration of the key signal at each field or frame. Further expansions of the wiped area, for showing more of the car, are indicated at 41 and 42, respectively, in FIGS. 5C and 5D. Finally, in FIG. 5E, the entire car, represented by reference numeral 43, is visible in the image.
Using the apparatus of FIG. 2, a "soft-edge" or a "painting effect" can be achieved in wipe effects such as that shown in FIGS. 5A-5E. Such a "painting effect" provides an attractively smooth or gradual transition, as with fine brush strokes, between a wiped portion of the video image and the balance of the image. This is accomplished by providing, as a key signal K, an analog signal having a level that varies between 0 and 1.
So long as the key signal is moving, as in the examples of FIGS. 4A-4B and 5A-5E, a "painting effect" with a smooth transition between the wiped area of the image and the balance of the image can be maintained. However, as will now be described with reference to FIGS. 6a-6i and also FIG. 2, when the key signal K is stationary, repeated application of the key signal to the signal fed back from video memory 37 causes the gradual, smooth painting effect to be lost and a sharp transition develops between the wiped area and the balance of the image.
In particular, FIGS. 6a and 6b respectively show waveforms for input video signal V.sub.1 and key signal K. The waveform of signal V.sub.2 output from multiplier 33 is given by the expression V.sub.2 =V.sub.1 .times.(1-K) and for present purposes this may be expressed as (1-K), as shown in FIG. 6c. The first frame output as video signal V.sub.4 is V.sub.4 (1)=(1-K), which is shown in FIG. 6d and represents the desired gradual smooth transition from the wiped area to the balance of the image.
The output signal V.sub.4 (1) for the first frame is fed back to multiplier 34 of key processor 32 and multiplied by key signal K to provide a signal V.sub.3 (1)=K-K.sup.2 (FIG. 6e), having peaks with an amplitude of about 0.25. The signal V.sub.3 (1) is summed at adder 36 with V.sub.2 =(1-K) resulting in the output signal V.sub.4 (2)=1-K.sup.2 as shown in FIG. 6f. The next cycle of feedback results in V.sub.3 (2)=K-K.sup.3 (FIG. 6g), with peaks having an amplitude of about 0.38. V.sub.2 is again added to V.sub.3 (2) at adder 36, to produce V.sub.4 (3)=1-K.sup.3 which is shown in FIG. 6h. As shown in FIG. 6i, if the feedback cycle continues n times (i.e., over n frames), with n being a relatively large number, the resulting output signal V.sub.4 (n)=1-K.sup.n results in an image that has a very sharp edge or gradient between the wiped portion of the image and the balance of the image. As a result, the desired gradual and smooth transition is lost. The increasingly sharp transition can be seen by comparing the waveforms of FIGS. 6d, 6f, 6h, and 6i.